You can create a conversion table from the Privilege Names used in the Defined Privileges document to the Id's used in PowerCLI with:
Get-VIPrivilege |Select-Object-Property Id,Name,Description |Sort-Object-PropertyId
In this table you can see that the Id of "Allow virtual machine download" is: VirtualMachine.Provisioning.GetVmFiles.
The Id of "Allow virtual machine files upload" is: VirtualMachine.Provisioning.PutVmFiles